In well operations, downhole electrical equipment or tools are often deployed in the wellbore on the end of a length of coiled tubing, for example for logging of the well, use of downhole cameras or well perforation. The prior art has taught a number of cable heads that provide a releasable connection between the coiled tubing and the downhole electronic tool in case the tool should be become stuck in the wellbore and that also receive the end of the coiled tubing electric line where the line's conductor is stripped of its external armor in order to electrically couple with the electrical components of the tool.
The disconnect function allowing release of the tool from the coiled tubing has been achieved at least in part by the use of shear pins interconnecting portions of the cable head housing so that when the tool becomes stuck, attempted retraction of the coiled tubing back toward the surface pulls on the cable head and the stuck tool coupled thereto until the tension in coiled tubing becomes sufficient to overcome the strength of the shear pins, which accordingly break and allow the upper portion of the housing to separate from the lower housing portion and the tool coupled thereto. The coiled tubing is drawn out of the well, leaving the stuck tool and coupled lower housing within the bore, which may later be retrieved with suitable fishing equipment.
U.S. Pat. No. 6,196,325, which is herein incorporated by reference, suggests problems with use of only such a shear pin connection in a separable cable head structure, in that inadvertent shearing and resulting disconnect may occur during perforating operations and that the tensile strength of the tubing needs careful consideration in selecting suitable shear pins to prevent inadvertent failure of the tubing string during pulling thereof in an attempted disconnection from the tool.
The above patent addresses these issues by employing a spring-biased piston than can be driven downward by pumping fluid down the tubing against to move into a position releasing lugs that otherwise lock the housing components together so that shear pins also connecting the housing components are only sheared once the operator has intentionally instigated a release function by pumping fluid downhole to build up a sufficient pressure to move the piston to the unlocking position releasing the lugs. To provide feedback at the surface on the position of the piston, initial movement thereof closes off through-ports in the housing to cease flow of the fluid until continued pumping builds up the pressure far enough to further displace the piston toward the unlocking position. While this closing of the fluid's flow path to cease circulation informs the operator of displacement of the piston, it also limits the flow rates at which the operator can pump down fluids through the tubing for purposes other than triggering the cable head's tool-release function. Also, the conductor of the electric line exits the cable armor near the top of the cable head, leaving it exposed through most of the line's passage through the cable and thus potentially susceptible to damage, wear or failure by exposure to fluid passing through the cable head.
Applicant has developed a unique cable head that not only provides a fluid-induced disconnect function to prevent inadvertent breakage of the shearable mechanical connection between the tubing and the tool, but also allows fluid circulation at flow rates beyond that which initializes the disconnect process, and protects the line conductor from exposure to the fluid.